The designation ".alpha..sub.1a " is the appellation recently approved to the IUPHAR Nomenclature Committee for the previously designated ".alpha..sub.1c " cloned subtype as outlined in the Pharmacological Reviews (Hieble, et al. (1995) Pharmacological Reviews 47: 267 270). The designation .alpha..sub.1a is used throughout this application and the supporting tables and figures to refer to this receptor subtype. At the same time, the receptor formerly designated .alpha..sub.1a was renamed .alpha..sub.1d. The new nomenclature is used throughout this application. Stable cell lines expressing these receptors are described herein; however, these cell lines were deposited with the American Type Culture Collection (ATCC) under the old nomenclature (infra).
Benign Prostatic Hyperplasia (BPH), also called Benign Prostatic Hypertrophy, is a progressive condition which is characterized by a nodular enlargement of prostatic tissue resulting in obstruction of the urethra. This results in increased frequency of urination, nocturia, a poor urine stream, and hesitancy or delay in starting the urine flow. Chronic consequences of BPH can include hypertrophy of bladder smooth muscle, a decompensated bladder, and an increased incidence of urinary tract infection. The specific biochemical, histological, and pharmacological properties of the prostate adenoma leading to the bladder outlet obstruction are not yet known. However, the development of BPH is considered to be an inescapable phenomenon for the aging male population. BPH is observed in approximately 70% of males over the age of 70. Currently, in the United States, the method of choice for treating BPH is surgery (Lepor, H., Urol. Clinics North Amer., 17: 651, 1990). Over 400,000 prostatectomies are performed annually (data from 1986). The limitations of surgery for treating BPH include the morbidity rate of an operative procedure in elderly men, persistence or recurrence of obstructive and irritative symptoms, as well as the significant cost of surgery. A medicinal alternative to surgery is clearly very desirable.
.alpha.-Adrenergic receptors (McGrath et al., Med. Res. Rev. 2, 407-533, 1989) are specific neuroreceptor proteins located in the peripheral and central nervous systems on tissues and organs throughout the body. These receptors are important switches for controlling many physiological functions and, thus, represent important targets for drug development. In fact, many .alpha.-adrenergic drugs have been developed over the past 40 years. Examples include clonidine, phenoxybenzamine and prazosin (for treatment of hypertension), naphazoline (a nasal decongestant), and apraclonidine (for treatment of glaucoma). .alpha.-adrenergic drugs can be broken down into two distinct classes: agonists (e.g., clonidine and naphazoline), which mimic the receptor activation properties of the endogenous neurotransmitter norepinephrine, and antagonists (e.g., pheoxybenzamine and prazosin), which act to block the effects of norepinephrine. Many of these drugs are effective, but also produce unwanted side effects (e.g., clonidine produces dry mouth and sedation in addition to its antihypertensive effects).
During the past 15 years, a more precise understanding of .alpha.-adrenergic receptors and their drugs has evolved through increased scientific scrutiny. Prior to 1977, only one .alpha.-adrenergic receptor was kown to exist. Between 1977 and 1988, it was accepted by the scientific community that at least two .alpha.-adrenergic receptors, .alpha..sub.1 and .alpha..sub.3, existed in the central and peripheral nervous systems. Since 1988, new techniques in molecular biology have led to the identification of at least six .alpha.-adrenergic receptors which exist throughout the central and peripheral nervous systems: .alpha..sub.1a (new nomenclature), .alpha..sub.1b, .alpha..sub.1d (new nomenclature), .alpha..sub.2a, .alpha..sub.2b and .alpha..sub.2c (Bylund, D. B., FASEB J 6: 832, 1992). In many cases, it is not known precisely which physiological responses in the body are controlled by each of these receptors. In addition, current .alpha.-adrenergic drugs are not selective for any particular .alpha.-adrenergic receptor. Many of these drugs produce untoward side effects that may be attributed to their poor .alpha.-adrenergic receptor selectivity.
Since the mid 1970's, nonselective .alpha. antagonists have been prescribed to treat BPH. In 1976, M. Caine et al. (Brit. J. Urol. 48: 955, 1976) reported that the nonselective .alpha.-antagonist phenoxybenzamine was useful in relieving the symptoms of BPH. This drug may produce its effects by interacting with .alpha.-receptors located on the prostate. However, this drug also produces significant side effects such as dizziness and aethenia, which severely limit its use in treating patients on a chronic basis. More recently, the .alpha.-adrenergic antagonists prazosin and torazosin have also been found to be useful for treating BPH. However, these drugs also produce untoward side effects. It has recently been discovered that the .alpha..sub.1a receptor is responsible for mediating the contraction of human prostate smooth muscle (Gluchowski, C. et al., WO 94/10989, 1994; Forray, C. et al., Mol. Pharmacol. 45: 703, 1994). This discovery indicates that the .alpha..sub.1a antagonists may be effective agents for the treatment of BPH with decreased side effects. Further studies have indicated that the .alpha..sub.1a receptor may also be present in other lower urinary tract tissues, such as urethral smooth muscle (Ford et al., Br. J. Pharmacol. 114; 24P, 1995).